1. Field of the Invention
The present invention relates to a fixing device for fixing an autofocus module to a mirror box of an SLR camera in which a quick-return mirror is accommodated.
2. Description of the Related Art
In typical SLR cameras having an autofocus system, a part of the quick-return mirror (main mirror) is formed as a half mirror portion while a sub-mirror is held by the quick-return mirror to be positioned behind the half mirror portion so that a light bundle of an object which is passed through the half mirror portion (hereinafter referred to as “object light bundle for autofocusing”) is reflected downwards by the sub-mirror to be incident on an AF (autofocus) module which includes a CCD line sensor and other optical elements. Conventionally, the angle of the sub-mirror with respect to the quick-return mirror is determined so that the object light bundle for autofocus is reflected downwards by the sub-mirror in a direction substantially orthogonal to the photographing optical axis (the optical axis of a photographing lens mounted to the camera body) when the quick-return mirror is in its initial position (position before a shutter release), and the AF module is fixed to an underside of the mirror box, in which the quick-return mirror is accommodated, so that the vertical position of the AF module can be adjusted with respect to the underside of the mirror box. Namely, the direction in which the position of the AF module can be adjusted is the same as the traveling direction of the object light bundle for autofocusing which has been reflected downwards by the sub-mirror toward the AF module, and such an object light bundle can be made to be incident precisely on the AF module by an adjustment of the position of the AF module.
In recent years there has been a tendency to increase the length of the sub-mirror to broaden an AF area (distance measuring area) in the vertical direction. To this end, the object light bundle for autofocusing is reflected downwards by the sub-mirror not in a direction orthogonal to the photographing optical axis but in a direction slightly oblique and forward of a direction orthogonal to the photographing optical axis to prevent the sub-mirror from interfering with the focal plane shutter, which is positioned behind the quick-return mirror.
In this case where the object light bundle for autofocusing is reflected downwards by the sub-mirror in a direction slightly oblique and forward of a direction orthogonal to the photographing optical axis (i.e., to the underside of the mirror box to which the AF module is fixed), the traveling direction of the object light bundle for autofocusing which has been reflected downwards by the sub-mirror to be incident on the AF module is not coincident with the direction in which the position of the AF module can be adjusted. This is of little importance as long as the deviation of the traveling direction of the object light bundle for autofocusing relative to the direction in which the position of the AF module can be adjusted is small. However, if the deviation is great, it is difficult to adjust the position of the AF module so that the object light bundle for autofocusing is properly incident on the AF module.